1. Field of the Invention
The present invention relates generally to a vane pump, and specifically to a vane pump, which can be effectively used in, for example, a fuel vapor leakage check module that checks fuel vapor leakage.
2. Description of Related Art
A known vane pump compresses and discharges fluid by rotating a rotor, which includes vanes and is received in a pump chamber of a casing. Japanese Unexamined Patent Publication No. 10-90107, which corresponds to U.S. Pat. No. 5,890,474, discloses one such vane pump, which is used in a fuel vapor leakage check module that checks leakage of fuel vapor from a fuel tank and which depressurizes or pressurizes the interior of the fuel tank. In this type of vane pump, a pump flow rate is important since the pump flow rate has a significant influence on the performance of the fuel vapor leakage check module.
In one previously proposed vane pump, bolts are installed through a casing and are threadably engaged with a mount of a motor, so that the casing is securely connected to the mount by the bolts. The casing makes flat surface contact with the mount, and the casing and the mount are tightly connected together by the bolts. Thus, when a degree of flatness of a contact surface of the casing and a degree of flatness of a contact surface of the mount, which contacts the contact surface of the casing, are relatively low, it is difficult to achieve tight contact between the casing and the mount around the bolts. For example, such a difficulty may arise in the case where a protrusion is formed in a position, which is remote from the receiving through holes in the casing. In such a case, the connecting force, which is achieved by the bolts to connect between the casing and the mount, decreases, and thereby the motor can be easily vibrated relative to the casing during operation of the vane pump. When this happens, an accidental change in the pump flow rate of the vane pump could occur.